Method of making methyl arylamines



UNITEDSTATES PATENT FFICE Patented Feb. 24,1931

EDGAR o. BRITTON Ann WILLIAM H. WILLIAMS, or MIDLAND, MICHIGAN, Assienons TO THE noWIoHnMIoAL COMPANY, or MIDLAND, MICHIGAN, A CORPORATION or p MICHIGAN q METHOD on MAKING METHY AnY'LAMINns The present invention relates to methods forthe preparation of methyl arylaminesby the interactionof an arylamine and methyl alcohol, and particularly to such methods wherein a relatively small, or catalytic,

amount of another methyl compound is emfployed to facilitatethe reaction.

In a pending application, Serial No.182,- 532, filed April 9, 1927, the present inventors have disclosed a metliod for the preparation of methyl anilines whereby a mixture of aniline andmethyl alcohol is heated with addi ,tion of a relativelysmall amount, i. e., from one to two per cent, ofmethyl bromide. We

r have now found'that the above method is applicable, withsuitable modifications, to y the preparation of N-methyl derivatives of arylamines in general. To the accomplishmerit of the foregoing and-related ends the invention, then, consists of the steps herein- U after fully clescribed and particularly pointed our in the claims, the. following description setting forth but a few of the various y'aryhmethyl ammonium bromide, such latter cOmporindthen being dissociated at the re- 1 "action temperature yielding the free methyl arylamine and methyl bromide. The course the reaction leading tothe formation, re

spectively, of a mono-methyl-or a dimethyl "arylarnine, maybe indicated by the Equanone (1) and (2),and (3), and (4) respectively, wherein R represents an aryl radical, vizw RNH i slz H nryl dimethyl amine antiwar- 13;

, 'Themethyi bromide I al'yl tri-methy] ammonium bromide R.N(CH 01-1 31 dimethyl arylamine may be introduced either assuch or by meansot a compound continuous stirring in an iron autoclavefor Q'A ncanon filed October 25, 1192s. Serial No. 315,099.

that will yield methyl bromide by dissociation during; the reaction, suchas an aryl or alkyl dior tri-niethyl ammonium bromide. Inasmuch as the methyl bromide is constantly re-formed during the process, j as shown in Equations (2) and (4),a relatively small amount thereof, c g., one to two per cent, based upon the weight of the arylamine, suffices for the complete conversion of the latter. it

Generally speaking, incarrying out our improved method or processfwc mixjone mole ot' arylaminelin which approximately from one to two per cent. of methyl bromide is admixed or dissolved, with somewhat more than the stoic'hiometrical proportion oi. methyl alcoholaccording to Equatio1is(1) The mixture is then heated with from 12 to20 hours at a, temperature be tween 200 and 260 C., preferably 220 to 240 C and at a pressure equal to or in eX- cess of that corresponding to the temperature. The separation of the reaction productsmay be effected either by distillation of the wholemass, or by mechanically separating the aqueous and, oily layers which are workedup individually. In the former procedure the excess methyl alcohol distills over first, then the water and finally the methylarylamine product is distilled over under reduced pressure. Most of the methyl bromide in the form of the quaternarycompound will be recovered in the still residue. When, on theother hand, the reaction mixture is allowed to stand, it separates into an aqueous alcohol and a methyl arylamine-alcohol layer. 1 Thelatter iswashed with water and distilled directly under vacuum. The wash water is added to the aqueous alcohol layer,

which contains all of the methylbromide in the form ofthe quaternary compound. Upon evaporating this solution for the recovery of alcohol substantiallyall ofthe methyl bromide, as thequaternary compound, remains in the residue from whichit is recovered and may be used for introduction into a succeeding operation in place of methyl bromide, in such case only sufiicient methyl bromide b ing added, to reaction mixture to make for losses." Ineither of the above procedures, the excess of methyl alcohol is recovered for use over again. 1

By way of illustration of our improved method or process, the following speclfic examples are given. Such examples are not to be understood as a limitation upon ourinvention, however, as itfis obvious thatthe present method is equally applicable to the preparation of other N' methyl-arylamines, and

derivatives thereof.

Example wZQ-A mixture of 1 mole paratoluidine, in which'was dissolved 2 per cent. of its weight of methyl bromide, and 3.3

moles methyl alcoholwas heated under pressure at a temperature of 230 C. for 20hours. The reaction product was separated into two layers, Upon distillation of the'oil layera v92 perv cent. ,yield of-dimethyl-para-toluidine, P. 209 (3., was obtained. An 85 per cent, recovery of excess methyl alcohol and 80 per cent. recoveryof organic bromide were also realized; v 0 I Example fl -A mixture of 1 mole a-naphthylamine, to which was added 2 per cent. of

its weight of methyl bromide, and 3.3 moles methyl alcohol was heated under pressure at 220 C. for 20 hours.- "The oil layer obtained from the reaction product yielded upon dis methyl-Denaphthylamine, B. P. 275 7 C.

tillation amixture of mono-methyland di- Upon separationof the latter ayield of 30 per cent. mono-methyland per cent. di-

methyl-a-naphthylamine was obtainec 1 :In either of the foregoing examples the methyl brom de is recovered in the form of a corresponding; aryl-methyl ammonium bro mide, which may beintroducedinto a succeed: ing operation for the methyl bromide therein.

lVhilethe examples specify 3.8 moles ,methyl alcoholfto one mole arylamine, this proportion maybe varied somewhat without materially affecting the result. In general from three to'four moles methyl alcohol to one of arylamine may be used whenthe' desired product isthe dimethyl-arylamine. By decreasing the relative amount of methyl alcohol taken for the reaction, and/or shortenmg the tune of reactiomun'der suitable-control, the method may be directed principally,

V orwholly, to the production of mono -metliyl-,

'desired, V v

We are: aware that it ha s b'een proposedto employ-iodine eompounds,e. g.', phenyl trimethyl ammonium iodide, as catalyst for the preparation of alkyl'anilines; as disclosed in i'nsteadoi dimethyl-, arylam'ine. -When both are producedtogether they may be subsequently separated by-the usual methods, if i U. S. Patent 1,413,494 to Rogers. Such proc V esses involving the use of iodine compounds, however, yield a product contaminated with I the iodine derivative which, can be removed only, by special andv costly procedure. The presence ofv the iodine compound .causes the methyl bromide therein.

methyl aniline so produced to darken rapidly on exposure to the air thusdetractmg trom its quality.

In contradistinction thereto, however, the method of the present invention makes use or methylbromide, or'a quaternary ammonium derivativev thereof. Not only is the advantage gained of employing a relatively less expensive material, but the product also has been-found to be otvery superior quality and can be exposed to the airfor longperiods of time without discoloration or'other detrimental efi'ect.

The termimethyl bromide compound em ployed in "certain ofthe'following 'clalms 1s vunderstood to includemethyl bromide or any 0 compound capable of yieldingjmeth'yl bro.- mide by dissociation or reaction during the operation of the herein disclosed method, as, for example, 'mon um bromide.

- claims or the equivalent: of such stated stepor steps be employed; I H llVeytherefore particularly po nt out and distinctly claim 7 as our. invention 1.. The method of making an N-methyl derivative of an arylamine which comprises reacting between such arylamlne and methyl alcohol with addition-ofxa relatively small 7 amount of methyl bromide.

2. The method of making an N-methyl derivative of an arylamine which comprises heating a mixture of such arylamine and ;methyl alcohol at a temperature between 200 and 260 C. and a corresponding pressure with addition of a relatively 7 small amount of methyl bromide. V

3. The method of making an rivative of an arylamine which comprises reacting between such arylamine and'methyl alcohol with [addition of a relatively small amount of .methyl bromide, recovering the quaternary aryl-methyl ammonium bromide from the reaction product and using such compound in a succeeding-operationforthe 4., The method of mal 'ng an N-methyl -derivative ofan arylamine' which comprises heating a mixture of such arylamine and methyl alcohol at a temperature between 200 and 260 C. and acorresponding pressure with addition of a relatively small amount of methyl bromide,..recovering the quaternary arylmethyl ammonium bromide from the reaction product' and' using such compound in a succeeding operation for'the methyl bromide therein.

5. The method of making an N-methyl derivative of an arylamine whiohcomprises reacting between such arylamine and methyl N-methyl dealcohol with addition of a relatively small amount of a methyl bromide compound.

6. The method of making an N-methyl derivative of an arylamine which comprises heating a mixture of such arylamine and bromide.

8. The method of making dimethyl-paratoluidine which comprises heating a mixture of paratoluidine and methyl alcohol at a temperature of about 230 C. and a corresponding pressure with addition of a relatively small amount of methyl bromide.

9. The method of making dimethyl-paratoluidine which comprises heating a mixture of one mole para-toluidine and from three to four moles methyl alcohol at a temperature of about 230 C. and a corresponding pressure with addition of a relatively small amount of methyl bromide.

10. The method of making dimethyl-parw toluidine which comprises heating a mixture of one mole para-toluidine and from three to four moles methyl alcohol at a temperature of about 230 C. and a corresponding pressure with addition of arelatively small amount of methyl bromide, recovering tolylmethyl ammonium bromide from the reaction product and using such compound in a succeeding operation for the methyl bromide therein.

.Signed by us this 17th day of October, 1928. i

EDGAR C. BRITTON. WILLIAMH. WILLIAMS. 

